The invention relates to the art of molding or sealing together the ends of plastic tubes using heat to provide a double-walled finished product which can be used in the manufacture of catheters or other devices for draining body cavities. High frequency induction heating is used to supply fast heat to the plastic tubes followed by rapid cooling of the tubes by circulating coolant through the mold in which the tubes are heated.
The invention is particularly useful for making double-walled tubes, such as, those disclosed in U.S. Pat. Nos. 3,108,595 and 3,241,554 to be used in body drainage devices, such as, catheters. In accordance with the disclosure of the first patent referred to, the tubes are made of rubber or nylon and may be fastened together by the interlocking method shown in FIG. 7. In this type of catheter, the tube ends must be fastened together so that the inner tube can be moved relative to the outer tube by pulling on it to expand flexible locking wings in the outer tube for locking the device in the body cavity during drainage. Processes for sealing the ends of concentric plastic tubes are disclosed in the second patent.
In sealing the ends of the concentric plastic tubes together, considerable difficulty has been experienced in the past due to the fact that it is difficult to mold the joint with sufficient plastic in the joint to provide the required strength to move the tubes relative to one another. This is particularly true when the materials of the tubes are of different plastics which have different melting points. It is very difficult to melt and incorporate enough plastic in the joint to make it sufficiently strong. To accomplish this it is necessary to heat the tube ends as rapidly as possible and to cool the melted plastic rapidly to attain sufficient plastic in the joint to make it strong. In medical applications wherein drainage tubes must be inserted in a chest cavity, for instance, it is necessary to have a sharp metal point associated with the drainage device to facilitate its insertion in the cavity. This requires a metal puncturing instrument in association with the drainage tube, and structure, such as a shoulder, must be provided inside the drainage tube against which the metal instrument or trochar seats for forcing the double-walled tube through the channel made by the trochar into the cavity to be drained.
Accordingly, it is an object of this invention to provide a method for sealing together the ends of two concentrically arranged plastic tubes to provide a strong joint.
It is another object to provide a method for making a combination double-walled drainage tube and metal trochar for use in drainage devices for draining body cavities.